Signal processing apparatus and method

A method of determining the relative position between first and second members which are relatively moveable in a measurement path, said first member comprising a plurality of sensing circuits, each extending along said measurement path and being offset from each other in said measurement path, said method comprising the steps of:

• using a generator on said second member to generate, in each of said sensing circuits, a time varying periodic carrier signal whose amplitude varies sinusoidally with the relative position between the second member and the respective sensing circuit on the first member, and wherein, due to the offset between said sensing circuits, the sinusoidal variation of the amplitude of the signals generated in said sensing circuits are out of phase with respect to each other;
• combining a first periodic time varying signal having the same period as said carrier signal with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said carrier signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;
• multiplying each of the signals generated in said plurality of sensing circuits with a respective one of the plurality of combined signals generated in said combining step;
• and
• adding the signals from said multiplying step to provide an output signal;
• wherein said predetermined phases of said plurality of second periodic time varying signals are determined so that said output signal from said adding means contains a single periodic component having the same predetermined period as said second periodic time varying signals and whose phase varies with the relative position between said first and second members.

A processing apparatus for processing a plurality of signals received from a position encoder used to encode the relative positions of two relatively movable members, wherein each of said plurality of signals varies sinusoidally with said relative position and out of phase with respect to each other, the apparatus comprising:

• means for combining a first periodic time varying signal having a first period with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said first periodic time varying signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;
• means for multiplying each of said received signals with a respective one of the plurality of combined signals generated by said combining means;
• and
• means for adding the signals from said multiplying means to provide an output signal, and wherein said predetermined phases of said periodically varying signals are determined so that, in use, the output signal from said adding means contains a single period whose phase varies with the relative position of the relatively moveable members.

A position detecting method comprising the steps of:

• providing first and second members that are movable relative to each other along a measurement path, said first member comprising a plurality of sensing circuits, each extending along said measurement path and being offset from each other in said measurement path and said second member comprising generating means for generating, in each of said sensing circuits, a time varying periodic carrier signal whose amplitude varies sinusoidally with the relative position between said generating means and the respective sensing circuit and wherein, due to the offset between said sensing circuits, the sinusoidal variation of the amplitude of the signals generated in said sensing circuits are out of phase with respect to each other;
• combining a first periodic time varying signal having the same period as said carrier signal with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said carrier signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;
• multiplying each of the signals generated in said plurality of sensing circuits with a respective one of the plurality of combined signals generated by said combining means;
• adding the signals from said multiplying step to provide an output signal;
• and
• determining the relative position of said first and second members using said output signal;
• wherein said predetermined phases of said plurality of second periodic time varying signals are determined so that said output signal from said adding step contains a single periodic component having the same predetermined period as said second periodic time varying signals and whose phase varies with the relative position between said first and second members.

A method of processing a plurality of signals received from a position encoder used to encode the relative positions of two relatively movable members, wherein each of the plurality of signals varies sinusoidally with said relative position and out of phase with respect to each other, the method comprising the steps of:

• combining a first periodic time varying signal having a first period with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said first periodic time varying signal and each having a different predetermined phase to generate a plurality of combined time varying signals;
• multiplying each of the received signals with a respective one of the plurality of combined signals generated in said combining step;
• and
• adding the signals from said multiplying step to provide an output signal, and wherein said predetermined phases of said periodically varying signals are determined so that the output signal from said adding step contains a single periodic component having said predetermined period whose phase varies with the relative position of the relatively movable members.